Fair Value Measurements - Reconciliation of Liabilities Measured at Fair Value on Quarterly Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in estimated fair value of convertible note payable	$ (1,811)	$ (12,118)	$ (1,145)
Fair Value, Inputs, Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at December 31, 2014	23,397
Change in estimated fair value of convertible note payable	1,811
Convertible note converted to shares of common stock	(25,208)
Balance at December 31, 2015	$ 0	$ 23,397